Dotnet stacks are missing logos

[deboer-tim]

/kind bug

Which area this bug is related to?

/area registry

What versions of software are you using?

n/a

Bug Summary

Describe the bug:
The Dotnet devfiles all have an invalid icon, which is showing up as a missing link on the devfile registry, VS Code explorer, etc.

To Reproduce:
Open the registry...

Expected behaviour

No missing link icons.

Any logs, error output, screenshots etc? Provide the devfile that sees this bug, if applicable.

Additional context

Suggestion on how to fix the bug

1. We should fix the links in these specific devfiles.
2. If an icon is missing we should show something other than the broken link - either use a placeholder or revert to what we do if there's no icon.

[kadel]

I have opened PR to fix icon links (devfile/registry#110)

2. If an icon is missing we should show something other than the broken link - either use a placeholder or revert to what we do if there's no icon.

+1 for having a fallback in case the icon is not reachable.

[schultzp2020]

fixed